Hydraulic vehicle brakes

ABSTRACT

To ensure adequate exercise of the seal of the intermediate piston means of a dual chamber hydraulic slave cylinder, the piston means is constructed as two separate piston members, axially movable relative to each other and normally urged apart by spring means, which may, e.g. be a belleville type or a coil compression spring. Interengaging spigot and socket means on the piston members may be provided to guide the two members and stabilize them against tipping movement.

United States Patent Gee et al. I

[ 51 Aug. 8, 1972 [54] HYDRAULIC VEHICLE BRAKES [72] Inventors: David William Gee; Michael Albert Carey, both of Kings Road, Tyseley, Birmingham 11, England 22 Filed:' Jan. 9, 1970' [21] Appl.No.: 1,753

[30] Foreign Application Priority Data Jan. 20, 1969 Great Britain...,...;....3,223/69 52 user. ..'.,...92/61,6( )/54.6 M, 188/345,

s11 Int.Cl ..F0lbl/02 [58] Field of Search @188/106 P, 152, 345,364, 363; 60/545 E, 54.6 E, 54.6 M; 277/59, 73; 92/61 56] References Cited UNITED STATES PATENTS 2,313,431 3/1943 Goepfrich 188/364 3,477,549 11/1969 Barton ..188/345 2,104,735 1/1938 Carrolletal ..'188/364X' 3,358,448 12/1967 l-Iufiman ..188/345 X FOREIGN PATENTS OR APPLICATIONS 779,383 l/ 1935 France ..188/363 646,824 11/1950 GreatBritain ..188/364 Primary Examiner-George E. A. Halvosa Attorney-Scrivener, Parker, Scrivener and Clarke 571 ABSTRACT To ensure adequate exercise of the seal of the intermediate piston means of a dual chamber hydraulic Y slave cylinder, the piston means is constructed as two separate piston members, axially movable relative to each other and normally urged apart by spring means,

which may, e.g. bea belleville type or a coil compressionspring. Interengag'ing spigot and socket means on the piston members may be provided to guide the two members and stabilize them against tipping movement.

6 Claims, 2 Drawing Figures HYDRAULIC VEHICLE BRAKES This invention relates to hydraulic vehicle brakes, and more particularly to dual slave cylinders for use in such brakes.

Dual slave cylinders are known in which an intermediate, floating piston is positioned in the cylinder between opposed actuating pistons to divide the cylinder space into two separate working chambers, one adjacent each piston and connected to separate pressure supplies. The intermediate piston serves to equalize the forces applied by the actuating pistons, ir-

respective of pressure difierences arising in service between the two working chambers. If the pressure supply to either chamber fails, the other supply can still provide the designed brake applying force to both shoes by virtue of outward movement of the floating piston in abutting engagement with the piston of the failed system. However, in normal operation, the intermediate piston may remain stationary for very long periods, and is liable to become corroded to the cylinder wall or for its seals to become weakened and, in some cases, locally adhered to the cylinder wall.

In accordance with the present invention, however, there is provided a dual slave cylinder for hydraulic wheel brake, comprising a cylinder body housing a pair of opposed actuating pistons at opposite ends of the cylinder, a pair of intermediate floating pistons dividing the cylinder space into two separate working chambers, one adjacent each actuating piston, the intermediate pistons being axially movable relative to each other, and resilient means acting between the two intermediate pistons and tending to urge them apart.

With this arrangement, the intermediate pistons are normally spaced apartby the resilient means, but are pressed against each other when the slave cylinder is pressurized, so as to provide some exercise of the intermediate piston seals, even when both working chambers are substantially equally pressurized (which will usually be the case during service brake operation). Without such exercise, the seals could eventually stick to the cylinder wall.

Preferably, the space between the two intermediate pistons, which is passive, is vented to atmosphere and the effective areas of the intermediate pistons are equal to the full cylinder area, to ensure maximum pressure differential, acting on each of the two pistons during hydraulic brake actuation.

Two forms of dual slave cylinder in accordance with the invention are described below, by way of example only, with reference to the accompanying drawings, in

which:

FIGS. 1 and 2 are axial sections of the respective slave cylinders.

The slave cylinder shown in FIG. 1 comprises a housing or cylinder body 10 having pressure inlets 11, 12

and housing an opposed pair of sealed, actuating 18, 19 apart, into abutting engagement with the respective actuating pistons 13, 14.

The intermediate pistons 18, 19 divide the cylinder space into two separate working chambers 26, 27, one adjacent each piston 13, 14 and served by the respective inlets ll, 12. The passive space 28 between the intermediate pistons is vented to atmosphere by a vent hole 29 open at all'times to atmosphere so as to prevent the buildup of pressure in the passive space.

The slave cylinder is shown in its normal, unpressurized condition. In service brake operation, both chambers 26 and 27 are supplied with fluid under pressure, which presses the pistons 18, 19 together, exercising the seals 20, 21, and forces the pistons 13, 14 outwardly to apply the brake shoes (not shown) engaged by tappets l6, 17. Should either hydraulic pressure system fail, the brakes are applied by the pressure in the other system, the pistons 18, 19 moving as'one to abut and force outwardly one piston 13 or 14. The spring washer 24 is of sufl'icient rigidity and suitable size to ensure that excessive pedal travel is not required to compress it as a prerequisite to brake application.

The slave cylinder shown in FIG. 2 is of generally similar construction and corresponding parts in FIGS. 1 and 2 are identified by like reference numerals.

In this embodiment, the pistons 18, 19 are of greater axial length, and the spigot and socket connection 22, 23 is omitted. This slave cylinder is designed for use in an internal shoe drum brake in which adjustment to compensate -for friction pad wear is effected at the center and one end of each shoe, so that one of the shoe-ends actuated by the cylinder is moved progressively outwardly, away from the cylinder, as adjustment is effected. There are two such cylinders in a drum brake installation.

The resilient means in this embodiment takes the form of a coil compression spring 30 of sufficient length to keep the intermediate pistons 18, 19 in contact with the respective actuating pistons l3, 14 throughout the range of available wear compensating adjustment. The left hand actuating piston 13 and intermediate piston 18 define between them a working chamber 26 of extended axial length, so that the piston 18 has sufficient movement to cater for adjustment and actuation before the piston seal 20 closes off the pressure inlet 11. Travel of the pistons 14 and 19 is limited by positive stop means, such as a circlip (split ring) 31. Operation of this slave cylinder is as described in relation to the cylinder of FIG. 1. I

In both embodiments, the effective area over which the two intermediate pistons are'exposed to atmospheric pressure is the full area of the cylinder. In the FIG. 1 embodiments the spigot 22- does not make a gas tight fit in socket 23, and in FIG. 2 it is apparent that the space 28 is bounded on one side by the full face of piston 19. As a result, the pistons are each subjected in use to the full difierence in pressure between the hydraulic pressure on one face and atmospheric pressure on the other, and this pressure difference acts over the full areas of the pistons.

We claim:

1. In a dual slave cylinder for an hydraulic wheel brake of the type which is connected to separate pressure supplies and includes a cylinder body having a cylinder space, a pair of opposed actuating pistons at 3 opposite ends of said cylinder space, intermediate, floating piston means in said cylinder space between said actuatingpistons to define therewith a pair of working chambers, oneadjacent each said actuating pistons, the improvement which comprises a pair of separate and individually sealed piston members constituting said floating piston means, said piston members being adapted for axial movement towards and away from each other and defining a passive cylinder space therebetween, vent means open at all times to atmosphere leading to said passive space for preventing the buildup of pressure therein, separate inlets to said working chambers including means for connecting said inlets to said separate pressure supplies, and spring means acting between said piston members to urge the same apart, said piston members being constructed and arranged to move slightly towards each other in opposition to said spring means upon delivery of pressure to the working chambers from said separate supplies so as to exercise the seals of said piston members and prevent said seals from sticking to the cylinder walls.

2. The improved slave cylinder of claim l,-wherein one said piston member has an axially directed socket and the other said piston member has an axially said spring means comprises a coilcompression spring I having opposite ends respectively engaging said piston members;

6. The improved slave cylinder of claim 5, wherein one said piston member has an axially directed socket for receiving and locating one end portion of said coil compression spring.

UNITED STATES PATENT OFTTCE QERTIFICATE 0F COEQTIUN Patent No. 3 682 049 Dated August 8 1972.

Inventor(s) David William Gee, et. a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet,- insert [73] Assignee Girling Limited Birmingham, England, a corporation of Great Britain Signed and sealed this 19th day of December 1972.

(SEAL) Attest:

EDWARD M.FLETCHER ,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM pomso (10'69) USCOMM-DC 0O376-P69 U.5. GOVERNMENT PNNTING OFFICE WDO-liS-SSJ. 

1. In a dual slave cylinder for an hydraulic wheel brake of the type which is connected to separate pressure supplies and includes a cylinder body having a cylinder space, a pair of opposed actuating pistons at opposite ends of said cylinder space, intermediate, floating piston means in said cylinder space between said actuating pistons to define therewith a pair of working chambers, one adjacent each said actuating pistonS, the improvement which comprises a pair of separate and individually sealed piston members constituting said floating piston means, said piston members being adapted for axial movement towards and away from each other and defining a passive cylinder space therebetween, vent means open at all times to atmosphere leading to said passive space for preventing the buildup of pressure therein, separate inlets to said working chambers including means for connecting said inlets to said separate pressure supplies, and spring means acting between said piston members to urge the same apart, said piston members being constructed and arranged to move slightly towards each other in opposition to said spring means upon delivery of pressure to the working chambers from said separate supplies so as to exercise the seals of said piston members and prevent said seals from sticking to the cylinder walls.
 2. The improved slave cylinder of claim 1, wherein one said piston member has an axially directed socket and the other said piston member has an axially directed spigot slidably engaged in said socket.
 3. The improved slave cylinder of claim 1, wherein said spring means comprises a frusto-conical spring washer inserted between said piston members.
 4. The improved slave cylinder of claim 1, wherein both of said piston members have pressure responsive areas equal to the full area of said cylinder space.
 5. The improved slave cylinder of claim 1, wherein said spring means comprises a coil compression spring having opposite ends respectively engaging said piston members.
 6. The improved slave cylinder of claim 5, wherein one said piston member has an axially directed socket for receiving and locating one end portion of said coil compression spring. 